c++: Add testcase for PR 90764.

     PR c++/90764
     * g++.dg/cpp1z/class-deduction69.C: New.

diff --git a/gcc/testsuite/g++.dg/cpp1z/class-deduction69.C b/gcc/testsuite/g++.dg/cpp1z/class-deduction69.C
new file mode 100644 (file)
index 0000000..8291f4a
--- /dev/null
+++ b/gcc/testsuite/g++.dg/cpp1z/class-deduction69.C
@@ -0,0 +1,12 @@
+// PR c++/90764
+// { dg-do compile { target c++17 } }
+
+namespace a {
+  struct b;
+  template <typename...> using c = b;
+}
+template <typename... d> struct e : a::c<d...> { // { dg-error "incomplete" }
+  using a::c<>::c;             // { dg-prune-output "not a base" }
+};
+template <template <typename> typename f> void g() { f(); }
+void h() { g<e>(); }